Abstract

Density-functional calculations clarify the role of an ultrathin layer on electrodes used in molecular electronics. The layer creates a sharp density of states, as in a scanning-tunneling microscope tip. The sharp , coupled with the of the molecule leads to negative differential resistance. Electron transfer between oriented molecules occurs via resonant tunneling. The characteristic for a thin-film of tris (8-hydroxyquinoline)-aluminum molecules, oriented using electric-field poling, is in excellent agreement with theory. This molecular is a robust, simple alternative to or mechanical break-junction structures.